Another question about no-fly times

[Cosmographer]

Thanks for the advice guys. Since I'd have 20-24 hours in between my Day 5 and Day 6 dives, I had assumed that I would be totally desaturated for the Day 6 dive. Apparently this is not the case, so I will cut the diving short by one day.

Just for the sake of knowledge, though, would most divers agree that had my Day 6 dive been the only dive of the trip (9meters/30 minutes), a 9 hour no-fly period would probably be sufficient? I've read other posts here by some highly respected SB'ers which have concluded that shallower dives - maybe 5 meters or so - wouldn't even require a no-fly period (if I remember correctly), despite DAN guidelines. This is just an effort to reconcile, for me, what initially appears to be contradicting opinions so that I can get a better understanding of the risks and tolerances involved.

 

[skankpile]

Will the computer be monitoring the ambient pressure out of water? Neither of mine activate unless the contacts get wet.

This was last weekend on a flight back from LAX (dove Catalina, and surrounding area) to Houston, TX: 737 ~38K feet pilot stated, and my cochran shows the cabin was pressurized to about 7K feet.

I took a monday afternoon flight to give me a 20hr window and Cochran said I'd be clear by 9hrs so I felt good about it...

The Cochran will stay on until the time to fly has ended. It will turn on any time you want it to, but not go into dive mode unless it senses water (it auto calculates salinity). It also monitors between dives so you can go into analyst (desktop application) and see the pressure changes and any flights you'd had between dives. A Cochran is not for everybody but its small for what it does and I keep using it for its advanced features... its a backup to my shearwaters.

I took the PO2 reading on an Analox ATA trimix analyzer I was carrying in my computer bag as you don't want the sensors in it banged around.

 

[boulderjohn]

Just to reply in general, looking at the original post and at your last modification, I would say there is a very good chance you would be OK. A very good chance.

Personally, I would not do it. But then, I don't go to Las Vegas, and I don't even do office football pools. If you are one of those who really likes that adrenaline rush that accompanies gambling, then you might really like the experience you are contemplating, even if the odds don't go your way.

BTW, to put this in perspective, when I say I would not do it, I will also say quite clearly that I think the rules as they are right now are quite conservative. I will also admit to driving home over mountain passes after a weekend of diving on more than a few occasions. A couple of years ago I drove home over those mountain passes after a pretty serious morning dive finishing off a three day weekend of serious dives, and I was perfectly fine. The buddy who accompanied me on every one of those dives was in the chamber for three days and took about 6 months to heal, but I was fine. It's like old Dirty Harry movie--"How lucky do I feel today?"

 

[rossh]

The problem is that if you do develop an injury - you can't get off the plane. It wont stop or divert to a nearby airport (if one exists in the middle of the Pacific). Even if they did stop at the next island, how are you going to get treated?

 

[japan-diver]

Why scuba for the dolphin dive? These are much better done snorkeling. Just swim with the dolphins on snorkel and you will be fine.

 

[Cosmographer]

Boulderjohn, I am usually pretty risk tolerant, but since my wife will be joining me on this trip, I would not go for it unless the chance of DCS in this situation was less than 5%. While we can't really gauge probability that accurately, the feeling I get from the posts here is that the chance of a hit will be considerably higher than that. I do like to gamble, but only at the $1 tables, hahaha.

Japan-diver, have you done the dolphin program in Palau? If so, how was the snorkeling encounter? I snorkeled with dolphins once in the open sea and couldn't get anywhere near photo-range because they stayed far below us most of the time. It just seems that diving with them would be more fun and better for pictures. (Also, we are not allowed to take pictures during the snorkel, but we can during the dive).

Based on the advice here, we can either do 4 diving days + 1 dolphin dive or 5 diving days + 1 dolphin snorkel. Still not sure which option would be best, but I guess that's getting a bit off-topic, lol.

 

[vladimir]

Boulderjohn, I am usually pretty risk tolerant, but since my wife will be joining me on this trip, I would not go for it unless the chance of DCS in this situation was less than 5%. While we can't really gauge probability that accurately, the feeling I get from the posts here is that the chance of a hit will be considerably higher than that. I do like to gamble, but only at the $1 tables, hahaha.

If you are comfortable with a 5% chance of DCS I think you are playing at the $500 table without knowing it. How many times do you have to entertain a 5% risk before it becomes a roughly 50-50 proposition?* Thirteen. For comparison, liveaboard divers have a DCS incidence of about .01%, on average.


*Assuming consecutive, independent, random trials.

 

[Cosmographer]

If you are comfortable with a 5% chance of DCS I think you are playing at the $500 table without knowing it.

No, I'm not comfortable with a 5% chance of DCS. I said less than 5%, and to be more specific, meant more like 1-2%, but I didn't bother getting that specific because it's a moot point anyway since there's no way we can calculate the likelihood of a hit with such accuracy. Perhaps a 1%-2% chance is still in the realm of "high-rollers", but I'm pretty comfortable with those odds.

 

[Karl_H]

Some interesting answers, I'd say the best reasoning so far is the dry gear without a doubt - wet gear is a pain in the a$$!

Once question is will you be using a Nitrox mix? If it's a live aboard with membranes you'll realistically be restricted to around 32-36%, at 9m that's a PPN2 of 1.2 for 36% at 9m or 0.96 at 5m. If you can get a higher mix you can keep the PPN2 to 0.79 at 9m using EAN58 or at 5m using EAN47. The PPN2 vs. tissue saturated pressures is what really controls on and off gassing, not the fact your underwater or above water.

Certifications may be an issue for the higher mixes though, EAN40 woild give 1.14 PPN2 at 9m and 0.9 PPN2 at 5m. If you use EAN40 and keep the dive to 5m I'd say you have no real additional worries in getting a flight 9 hours later, if you are still worried there also the 100% pure O2 for an hour on the surface option which should help.

There's also the ratio deco approach, that is now even promoted with zero no fly time after diving (although I'm not too confident about the experimental scientific research to back it up), however the available 9 hours gives you quite a buffer.

There's also the fitness, age, hydration, fatigue etc. issue to bear in mind also. If you really want to do the dive consider the above, but it would have seemed easier to just adjust the flight beforehand - that way you get dry gear too

Karl

 

[Searcaigh]

No, I'm not comfortable with a 5% chance of DCS. I said less than 5%, and to be more specific, meant more like 1-2%, but I didn't bother getting that specific because it's a moot point anyway since there's no way we can calculate the likelihood of a hit with such accuracy. Perhaps a 1%-2% chance is still in the realm of "high-rollers", but I'm pretty comfortable with those odds.

My comfort zone is 0% risk of DCS

What is that phrase again? ...... "There are old divers and bold divers, but no old bold divers!"